Combined Biophysical Chemistry Reveals a New Covalent Inhibitor

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Biophysical Chemistry, Biomolecules, and Biomaterials; Surfactants and Membranes

Combined Biophysical Chemistry Reveals the Finding of a New Covalent Inhibitor with a Low-Reactive Alkyl Halide Tang Li, Rene Maltais, Donald Poirier, and Sheng-Xiang Lin J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.8b02225 • Publication Date (Web): 27 Aug 2018 Downloaded from http://pubs.acs.org on August 28, 2018

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The Journal of Physical Chemistry Letters

Combined Biophysical Chemistry Reveals the Finding of a New Covalent Inhibitor with a LowReactive Alkyl Halide Tang Li †‡, René Maltais†, Donald Poirier*†‡ and Sheng-Xiang Lin*†‡ †

CHU de Québec - Research Center, 2705 Boulevard Laurier, Québec, QC G1V 4G2, Canada



Faculty of Medicine, Université Laval, Québec, QC, Canada

AUTHOR INFORMATION Corresponding Author *

S.X.L.,

Tel.:

+1-418-525-4444

x42296/x46377,

fax:

+1-418-654-2298,

E-mail:

[email protected]; D.P., Tel.: +1-418-525-4444 x46427, fax: +1-418-654-2298, E-mail: [email protected]

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Abstract 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1) plays a pivotal role in the progression of estrogen-related diseases due to its involvement in the biosynthesis of estradiol (E2), constituting a valuable therapeutic target for endocrine treatment. In the present study, we successfully cocrystallized the enzyme with the reversible inhibitor 2-methoxy-16β-(m-carbamoylbenzyl)-E2 (2-MeO-CC-156) as well as the enzyme with the irreversible inhibitor 3-(2-bromoethyl)-16β-(mcarbamoyl benzyl)-17β-hydroxy-1,3,5(10)-estratriene (PBRM). The structures of ternary complexes of 17β-HSD1-2-MeO-CC-156-NADP+ and 17β-HSD1-PBRM-NADP+ comparatively show the formation of a covalent bond between His221 and the bromoethyl side chain of the inhibitor in the PBRM structure. A dynamic process including benefit molecular interactions that favor the specific binding of a low-reactive inhibitor and subsequent N-alkylation event through the participation of His221 in the enzyme catalytic site clearly demonstrates the covalent bond formation. This finding opens the door to a new design of alkyl halide-based specific covalent inhibitors as potential therapeutic agents for different enzymes, contributing to the development of highly efficient inhibitors.

TOC GRAPHICS

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KEYWORDS: Irreversible inhibitors, 17β-hydroxysteroid dehydrogenase 1, N-alkylation, cocrystallization, estrogen-related diseases Covalent inhibitors (CI) are more beneficial than non-covalent ones, such as a reduced risk of drug resistance, extended inhibition effect, increased efficiency with lower doses and less side effects.1 However, despite these advantages, toxicity issues encountered with the first generation of CI related to their high reactivity, low specificity of action, and some immunogenicity response produced resistance from pharmaceutical industry.2 Nevertheless, the approval of more specific and safe targeted covalent inhibitors in the last decade leads to a resurgence of interest in the pharmaceutical research field.3-4 However, the design of such inhibitors remains a challenge, considering that a high-binding affinity for the targeted protein, as well as an inherent reactivity, are two essential elements that must be combined in a single molecular entity to obtain a valuable drug candidate. Even if some covalent drugs have been documented bearing a low reactive group that could lead to alkylation in a particular molecular context,5 the electrophilic group incorporated into CI are generally highly reactive (α,β-unsaturated ketone, α-haloketone, cyanamide, fluorophosphate, and epoxide), with the inconvenience of increasing the risk of offtarget and non-specific tagging.6 The use of less reactive electrophile groups is thus suitable for increasing the level of CI specificity.2, 7-9 Most CI drugs are based on the reactivity of cysteine,10 the strongest nucleophile among natural amino acid (AA), allowing the alkylation of a large diversity of electrophiles.11 However, because of its low abundance or an inaccessible position in the enzyme catalytic site, other nucleophilic residues have been exploited for covalent inhibition such as lysine, serine, tyrosine, threonine, aspartate and glutamate.12-13 One uncommon case is the histidine (His) residue, which,

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despite of its good nucleophilicity and its presence at catalytic site of many enzymes,14 has been very rarely exploited in CI design.15 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1) catalyzes the final step of the transformation of estrone (E1) to estradiol (E2), the most potent estrogen, and is considered a promising therapeutic target for endocrine treatment.16-21 This enzyme also catalyzes the reduction of dehydroepiandrosterone (DHEA) into 5-androstene-3β,17β-diol (5-diol) and dihydrotestosterone (DHT) into 5α-androstane-3β,17β-diol (3β-diol), which has been suggested to become more important after menopause, and may be involved in aromatase inhibitor resistance.16, 21-23 It is well known that E2 stimulates breast cancer, and also plays a crucial role in other estrogen-related diseases such as ovarian cancer, endometriosis, and endometrial cancer.24-25 Thus, the blockade of the biosynthesis of E2 is considered to be a valuable therapeutic approach for treating estrogen-dependent diseases.24-26

Figure 1. Three potent steroidal inhibitors of 17β-HSD1: 16β-(m-carbamoylbenzyl)-E2 (CC156). 2-methoxy-16β-(m-carbamoylbenzyl)-E2 (2-MeO-CC-156) and 3-(2-bromoethyl)-16β-(mcarbamoyl benzyl)-17β-hydroxy-1,3,5(10)-estratriene (PBRM). Previous reports have described 16β-(m-carbamoylbenzyl)-E2 (CC-156) (Figure 1) as a potent competitive and reversible inhibitor of 17β-HSD1 with an IC50 value of 44 nM.27 Unfortunately, this compound has an estrogenic activity observed by the proliferation of the stimulation of

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estrogen receptor (ER) positive cell lines MCF-7 and T-47D.27 To reduce this unwanted estrogenic activity, further development was then engaged to modify the E2 scaffold of CC-156. The addition of a methoxy (MeO) group at position C-2 of CC-156, which produced 2-MeO-CC156 (Figure 1), was efficient in attenuating estrogenic activity, but was unfavorable for enzyme inhibition.27 A more promising strategy next focused on the chemical modification of the C-3 phenolic group, which is known to be important for the binding of the E2 scaffold to ER,28 and resulted in the discovery of PBRM (Figure 1), the first non-estrogenic irreversible inhibitor of 17β-HSD1.29 Further investigations demonstrated the PBRM efficiency in both breast cancer cells and human breast tumor xenografts in nude mice,30-31 as well as interspecies differences of 17β-HSD1 inhibition.32 Kinetic studies classified PBRM as a competitive and irreversible inhibitor of 17β-HSD1 and a covalent binding of PBRM with 17β-HSD1 was then demonstrated by using a 17α-tritiated derivative of PBRM.32 Furthermore, a molecular modeling study investigating interspecies inhibitory activity of PBRM pointed out His221 as a potential key AA involved in the formation of a covalent bond with the bromoethyl side chain. Interestingly, as an indication of the applicability of the bromoethyl group for developing a specific CI drug, PBRM possesses the expected properties of a CI, such as an extended inhibition action and a very low promiscuity rate.33 The bromoethyl side chain also provides a reduced in vitro CYP’s metabolism in comparison to its phenolic analog (CC-156), which is translated by a higher in vivo bioavailability for PBRM.29 Despite the indirect evidence of an alkylation between PBRM and 17β-HSD1, the existence and the exact configuration of expected covalent bonds remain to be proven. This was especially significant, considering the predicted low reactivity between a His residue and a primary alkyl halide, even more in a physiological environment.32 Obviously, the demonstration of the capacity

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of a common and accessible functional group like a primary alkyl halide to act as a reagent for the N-alkylation of an enzyme could demonstrate the viability of such a weak electrophile group for the development of a new type of selective CI. In fact, very few documented examples of an enzyme alkylation by a primary alkyl halide derivative have been reported to date, including a case of O-alkylation from a carboxylate group of Asp106 residue for haloalkane dehalogenase tagging,34 and a suspected S-alkylation from Met193 of 16α-bromopropyl-E2 leading to an irreversible inhibition of 17β-HSD1.35-36 Importantly, the primary alkyl halide electrophile group must not be confused with activated alkyl halide units, like the highly reactive N-ethylhalide of "Nitrogen mustard" agents, which form a covalent bond via the formation of an intermediate aziridinium very reactive species that reacts with the DNA nitrogenous base,37 or with benzyl halide38-39 and α-halo ketone40 groups, which are not specific, albeit useful in labeling affinity agents for enzyme characterization.41-42 Since no example of N-alkylation between a enzyme and a primary alkyl halide has been reported to date and also to rule out the possibility of the Met279 of 17β-HSD1 to act as nucleophile over the primary alkyl halide (Figure S1), we thus seized this opportunity and engaged co-crystallization experiments of PBRM with 17β-HSD1 to prove the capacity of such a weak electrophile to form a covalent bond with the suspected His221 residue, an AA rarely exploited in design of CI drugs.15

Table 1. Data collection and refinement statistics 17β-HSD1-2-MeO-CC-156-

17β-HSD1-PBRM-

+

NADP+

P212121

P212121

NADP Data Collection Space group

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Unit cell a,b,c (Å)

41.75, 107.98, 115.72

42.82, 108.94, 116.36

α,β,γ (°)

90, 90, 90

90, 90, 90 a

Resolution range (Å)

25-2.10 (2.21-2.10)

25-2.2 (2.32-2.20)

Number of reflections

173088 (23506)

184811 (24512)

Unique reflections

28809 (3929)

28372 (4006)

Completeness (%)

91.9 (87.7)

99.5 (98.1)

I/σ(I)

7.4 (3.2)

11.0 (3.4)

Rmeansb

0.144 (0.456)

0.108 (0.521)

Multiplicity

6.0 (6.0)

6.5 (6.1)

Wilson B-factor (Å2)

27.5

33.0

R-workc

0.21

0.23

R-freed

0.26

0.30

Bond lengths (Å)

0.013

0.011

Bond angles (°)

1.79

1.68

Most favored regions

93.9

93.3

Additional allowed regions

6.1

6.5

Generously allowed regions

0.0

0.2

Disallowed regions

0.0

0.0

39.0

47.0

Refinement

r.m.s.d

Ramachandran plote (%)

Average B, all atoms (Å2) a b

Data statistics for the outer shell are given in parentheses. The

redundancy-independent

Rmerge/Rsym,



 = ∑  ∑ , − 〈  〉 /

∑ ∑ , c  = ∑ | (ℎ !)| − |## (ℎ !)| / ∑| (ℎ !)| d Rfree = the cross-validation R factor for 5% of reflections e Calculated with PROCHECK43

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Figure 2. View of the active sites within the A subunit of 2-MeO-CC-156 (A) and PBRM (B) ternary complex structures. Inhibitor 2-MeO-CC-156 (F0A) and PBRM (F0D), and cofactor NADP+ are shown in their omit Fo-Fc and 2Fo-Fc electron densities. The side chains of important residues Leu95, Ser142, Asn152, Tyr155, His221, and Glu282 are shown in their 2Fo-Fc electron densities. 2Fo-Fc maps draw in gray and contoured at 1σ; Fo-Fc maps draw in green and contoured at 2.5σ. The backbone of the A subunit in 2-MeO-CC-156 and PBRM complexes are shown in magenta and blue cartoon, respectively. The space group identified for all the crystals was P212121 with a dimer in one asymmetric unit representing the functional unit of the enzyme.44-45 Two ternary complexes, 17β-HSD1-2-MeO-

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CC-156-NADP+ and 17β-HSD1-PBRM-NADP+, were refined to 2.1 and 2.2 Å, respectively. The two models show good stereochemistry46 and the quality of the final refined models can be accessed from the statistics in Table 1. The models of 17β-HSD1 with PBRM (F0D) and 2-MeOCC-156 (F0A) ternary complexes show very clear electron density for almost all residues, except for the C-terminal end of the protein (residues 286-327) as well as the flexible loop region from Ala191 to Gly198, as observed in other 17β-HSD1 complexes.21, 47-49 The active-site structure of both inhibitor complexes for the A subunit is shown in Figure 2.

Figure 3. Superposition of A subunit of 2-MeO-CC-156 (magenta) and PBRM (blue) ternary complexes along with 17β-HSD1-CC-156-NADP+ (pink) at the binding sites, showing the

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inhibitors and important residues. A) Superposition of 2-MeO-CC-156 and CC-156 complexes at the steroid binding site. B) Superposition of PBRM and CC-156 complexes at the steroid binding sites. Interacting residues are labeled and shown in sticks. Hydrogen bonds of inhibitor 2-MeOCC-156 and PBRM with their surrounding residues are presented in green dashed lines. Several important distances are labeled and indicated in black dashed lines. The presence of a methoxy group at position C-2 in 2-MeO-CC-156 introduces a strong hydrophobic interaction with residue Leu262 with the distance of 3.15 Å between C-32 (CH3 of MeO) of inhibitor and Cδ of the AA residue. This interaction causes the inhibitor to shift 1.04 Å at the O-4 end, and to rotate by approximately 4.8º at the steroid core and 3.5º at the benzylamide ring, as compared to the position of CC-156 complex when superimposing the 2-MeO-CC-156 complex with the previously reported CC-156 ternary complex (PDB ID 3HB5) by Cα atoms (Figure 3A).50 The side chain of Glu282, used to make a hydrogen bond with the inhibitor in the CC-156 ternary complex adopts a conformation facing the outside of the protein. Thus, no hydrogen bond can form between the AA residue and 2-MeO-CC-156. Besides, the movement of the O-4 at the end of 2-MeO-CC-156 forces the imidazole side chain of His221 to shift away by 1.49 Å for the Nε as compared with the position of the Cε of His221 in CC-156 complex. The hydrogen bond between the inhibitor and His221, which is important for ligand recognition and orientation,51 is established in 2-MeO-CC-156 complex with a distance of 2.86 Å (Table S1). However, the movement of the side chain of His221 toward the solvent leading to the decrease of its stability (average B-factor 49.0 Å2 of the AA residue as compared with 39.0 Å2 of the subunit) compared with its counterpart (average B-factor 30.7 Å2 of the AA residue as compared with 29.8 Å2 of the subunit) in the CC-156 complex.50 Indeed, when 0.1 µM inhibitor concentration was used, 2-

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MeO-CC-156 inhibited 37% of the transformation of E1 into E2, whereas CC-156 inhibited 77% of the same reaction.27 This is in agreement with the relatively high flexibility of the bound 2MeO-CC-156 (average B-factor 54.9Å) as compared to CC-156 (average B-factor 35.6Å). The hydrogen bonding with Ser142 is conserved in the 2-MeO-CC-156 complex, as in the CC-156 ternary complex. For the benzamide ring, the π-π interaction between Tyr155 and the ring is conserved (Figure 3A). The distance between Cε2 of Tyr155 and C-23 of 2-MeO-CC-156 is 3.50 Å and the distance between the centroid of the two phenyl rings is about 4.4 Å, a little bit longer, compared with the distances observed in the CC-156 ternary complex (4.3 Å). Nevertheless, three hydrogen-bonds between the carboxamide group of the inhibitor and Leu95 and Asn152 residues are presented (Figure 3A and Table S1). However, it is more reasonable that the O-29 of the carboxamide (CON) group of the inhibitor acts as an acceptor forming a hydrogen bond with N of Leu95 whereas the N-30 (CON) acts as a donor forming two hydrogen bonds with O of Leu95 and Oδ of Asn152 (Table S1). Thus, the CON group in 2-MeO-CC-156 adopts a conformation of 180º flip, as compared with that in the CC-156 ternary complex (Figure 3A). In the 17β-HSD1-PBRM-NADP+ ternary structure, an unambiguous continuity of electron density from the side chain of His221 to the bound PBRM is observed in both subunits, indicating the formation of a covalent bond between the Nε of His221 and the C-31 (BrCH2) of PBRM (Figure 2B). Structure overlay of the complex with CC-156 complex shows a slight shifting at the C-3 end of PBRM (0.66 Å) as well as the imidazole side chain of His221 (0.89 Å) as compared with the positions of their counterparts in the CC-156 complex, indicating the dynamic process favoring the formation of the covalent bond between them. The slight movement of the steroid core of PBRM and side chain of His221 is caused by the formation of their covalent bond

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(Figure 3B). As a result, the distance of the hydrogen bond between O-19 of the inhibitor and Oγ of Ser142 increased to 3.22 Å (Table S1). The hydrogen bond with Ser142 is one of the three major interactions that the potent inhibitor CC-156 interacts with 17β-HSD1,30 the increased distance of the bond thus indicating a less favored interaction of the inhibitor with the enzyme. Similar to CC-156 and 2-MeO-CC-156 complexes, the π-π interaction between the benzylamide ring of PBRM and the side chain of Tyr155 is conserved. The distance between Cε2 of Tyr155 and C-23 in the benzylamide ring of PBRM (3.35 Å) is slightly shorter than that in both the CC-156 (3.45 Å) and 2-MeO-CC-156 (see above) complexes. Besides, the distance of the centroid of the two phenyl rings (4.32 Å) is almost the same as in the CC-156 complex. The carboxamide group of PBRM adopts the same conformation as 2-MeO-CC-156 described previously, making three hydrogen bonds with Leu95 and Asn152 residues (Figure 3B). The distance of the three hydrogen bonds in the PBRM complex is similar to that in the CC-156 complex (Table S1), indicating their important role in the inhibitor binding to the enzyme. These molecular interactions are thus sufficiently favorable to bring the bromoethyl side chain of PBRM in proximity to His221 and to favor the reaction between these two complementary groups. In fact, such a reaction between an alkyl halide and a relatively poor nucleophile like His is not possible under physiological conditions. Even in the laboratory, excess amounts of imidazole or His were found to be unable to react with PBRM at room temperature.32 The proximity effect is thus a crucial factor to allow this unfavorable event, as it has been previously demonstrated for low reactive electrophile groups in CI reactivity.9 In conclusion, the present study illustrates the structural details of different inhibitory mechanisms of two potent 17β-HSD1 inhibitors, the reversible inhibitor 2-MeO-CC-156 and the irreversible inhibitor PBRM, as compared to CC-156. The results strongly support PBRM as a

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promising and selective new drug candidate for the adjuvant therapy of estrogen-dependent diseases. All these represent a breakthrough for the long history of 17β-HSD1 inhibitor search. Also, and in a broader way, this is the first report of a specific N-alkylation between a His residue and a low reactive alkyl halide-based inhibitor, which supports the viability of such an approach toward the development of specific CI. EXPERIMENTAL METHODS 17β-HSD1 was expressed by baculovirus expression system and purified by a procedure comprising two chromatographic steps: Blue-Sepharose affinity, and Q-Sepharose anion exchange columns, as described previously.52-53 The full details of 17β-HSD1 expression, purification and co-crystallization with inhibitor 2-MeO-CC-156 and PBRM are provided in the SI. The in silico analysis of PBRM interacting with 17β-HSD1 before the His221 N-alkylation is described in the SI.

ASSOCIATED CONTENT Supporting Information. Experimental Procedures, figure illustrating in silico analysis of CI and enzyme interactions before the alkylation event, tables presentation of hydrogen bond interaction. The Supporting Information is available free of charge via the Internet at http://pubs.acs.org.

Notes The authors declare no competing financial interests.

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The PDB ID of 17β-HSD1-2-MeO-CC-156-NADP+ and 17β-HSD1-PBRM-NADP+ are 6CGC and 6CGE, respectively.

ACKNOWLEDGMENT The authors would like to acknowledge the CIHR’s support (MOP97917) to Sheng-Xiang Lin, Donald Poirier and Charles Jean Doillon.

REFERENCES (1) Bauer, R. A. Covalent Inhibitors in Drug Discovery: from Accidental Discoveries to Avoided Liabilities and Designed Therapies. Drug. Discov. Today 2015, 20, 1061-1073. (2) Johnson, D. S.; Weerapana, E.; Cravatt, B. F. Strategies for Discovering and Derisking Covalent, Irreversible Enzyme Inhibitors. Future Med. Chem. 2010, 2, 949-964. (3) Singh, J.; Petter, R. C.; Baillie, T. A.; Whitty, A. The Resurgence of Covalent Drugs. Nat. Rev. Drug. Discov. 2011, 10, 307-317. (4) Baillie, T. A. Targeted Covalent Inhibitors for Drug Design. Angew. Chem., Int. Ed. Engl. 2016, 55, 13408-13421. (5) Lei, J.; Zhou, Y.; Xie, D.; Zhang, Y. Mechanistic Insights into a Classic Wonder Drug-Aspirin. J. Am. Chem. Soc. 2015, 137, 70-73. (6) De Cesco, S.; Kurian, J.; Dufresne, C.; Mittermaier, A. K.; Moitessier, N. Covalent Inhibitors Design and Discovery. Eur. J. Med. Chem. 2017, 138, 96-114. (7) Lopes, F.; Santos, M. M. M.; Moreira, R. Designing Covalent Inhibitors: A Medicinal Chemistry Challenge. In Biomedical Chemistry: Current Trends and Developments; Vale, N., Ed.; De Gruyter Open Ltd: Warsaw/Berlin, 2015; pp 44-59. (8) Long, M. J. C.; Aye, Y. Privileged Electrophile Sensors: A Resource for Covalent Drug Development. Cell Chem. Biol. 2017, 24, 787-800. (9) Kobayashi, T.; Hoppmann, C.; Yang, B.; Wang, L. Using Protein-Confined Proximity to Determine Chemical Reactivity. J. Am. Chem. Soc. 2016, 138, 14832-14835. (10) Backus, K. M.; Correia, B. E.; Lum, K. M.; Forli, S.; Horning, B. D.; Gonzalez-Paez, G. E.; Chatterjee, S.; Lanning, B. R.; Teijaro, J. R.; Olson, A. J., et al. Proteome-Wide Covalent Ligand Discovery in Native Biological Systems. Nature 2016, 534, 570-574. (11) Marino, S. M.; Gladyshev, V. N. Analysis and Functional Prediction of Reactive Cysteine Residues. J. Biol. Chem. 2012, 287, 4419-4425. (12) Shannon, D. A.; Weerapana, E. Covalent Protein Modification: The Current Landscape of Residue-Specific Electrophiles. Curr. Opin. Chem. Biol. 2015, 24, 18-26. (13) Powers, J. C.; Asgian, J. L.; Ekici, O. D.; James, K. E. Irreversible Inhibitors of Serine, Cysteine, and Threonine Proteases. Chem. Rev. 2002, 102, 4639–4750.

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(14) Liao, S. M.; Du, Q. S.; Meng, J. Z.; Pang, Z. W.; Huang, R. B. The Multiple Roles of Histidine in Protein Interactions. Chem. Cent. J. 2013, 7, 44. (15) Liu, S.; Widom, J.; Kemp, C. W.; Crews, C. M.; Clardy, J. Structure of Human Methionine Aminopeptidase-2 Complexed with Fumagillin. Science 1998, 282, 1324-1327. (16) Lin, S. X.; Chen, J.; Mazumdar, M.; Poirier, D.; Wang, C.; Azzi, A.; Zhou, M. Molecular Therapy of Breast Cancer: Progress and Future Directions. Nat. Rev. Endocrinol. 2010, 6, 485493. (17) Moeller, G.; Adamski, J. Integrated View on 17beta-Hydroxysteroid Dehydrogenases. Mol. Cell Endocrinol. 2009, 301, 7-19. (18) Lin, S. X.; Poirier, D.; Adamski, J. A Challenge for Medicinal Chemistry by the 17βHydroxysteroid Dehydrogenase Superfamily: An Integrated Biological Function and Inhibition Study. Curr. Top. Med. Chem. 2013, 13, 1164-1171. (19) Aka, J. A.; Zerradi, M.; Houle, F.; Huot, J.; Lin, S. X. 17beta-Hydroxysteroid Dehydrogenase Type 1 Modulates Breast Cancer Protein Profile and Impacts Cell Migration. Breast Cancer Res. 2012, 14, R92. (20) Zhang, C. Y.; Chen, J.; Yin, D. C.; Lin, S. X. The Contribution of 17beta-Hydroxysteroid Dehydrogenase Type 1 to the Estradiol-Estrone Ratio in Estrogen-Sensitive Breast Cancer Cells. PLoS One 2012, 7, e29835. (21) Aka, J. A.; Mazumdar, M.; Chen, C. Q.; Poirier, D.; Lin, S. X. 17beta-Hydroxysteroid Dehydrogenase Type 1 Stimulates Breast Cancer by Dihydrotestosterone Inactivation in Addition to Estradiol Production. Mol. Endocrinol. 2010, 24, 832-845. (22) Simard, J.; Vincent, A.; Duchesne, R.; Labrie, F. Full Oestrogenic Activity of C19-∆5 Adrenal Steroids in Rat Pituitary Lactotrophs and Somatotrophs. Mol. Cell Endocrinol. 1988, 55, 233-242. (23) Hanamura, T.; Niwa, T.; Gohno, T.; Kurosumi, M.; Takei, H.; Yamaguchi, Y.; Ito, K.; Hayashi, S. Possible Role of the Aromatase-Independent Steroid Metabolism Pathways in Hormone Responsive Primary Breast Cancers. Breast Cancer Res. Treat. 2014, 143, 69-80. (24) Marchais-Oberwinkler, S.; Henn, C.; Moller, G.; Klein, T.; Negri, M.; Oster, A.; Spadaro, A.; Werth, R.; Wetzel, M.; Xu, K., et al. 17beta-Hydroxysteroid Dehydrogenases (17beta-HSDs) as Therapeutic Targets: Protein Structures, Functions, and Recent Progress in Inhibitor Development. J. Steroid Biochem. Mol. Biol. 2011, 125, 66-82. (25) Poirier, D. 17β-Hydroxysteroid Dehydrogenase Inhibitors: A Patent Review. Expert. Opin. Ther. Pat. 2010, 20, 1123-1145. (26) Brodie, A.; Njar, V.; Macedo, L. F.; Vasaitis, T. S.; Sabnis, G. The Coffey Lecture: Steroidogenic Enzyme Inhibitors and Hormone Dependent Cancer. Urol. Oncol. 2009, 27, 5363. (27) Laplante, Y.; Cadot, C.; Fournier, M. A.; Poirier, D. Estradiol and Estrone C-16 Derivatives as Inhibitors of Type 1 17β-Hydroxysteroid Dehydrogenase: Blocking of ER+ Breast Cancer Cell Proliferation Induced by Estrone. Bioorg. Med. Chem. 2008, 16, 1849-1860. (28) Fang, H.; Tong, W.; Shi, L. M.; Blair, R.; Perkins, R.; Branham, W.; Hass, B. S.; Xie, Q.; Dial, S. L.; Moland, C. L., et al. Structure−Activity Relationships for a Large Diverse Set of Natural, Synthetic, and Environmental Estrogens. Chem. Res. Toxicol. 2001, 14, 280-294. (29) Maltais, R.; Ayan, D.; Trottier, A.; Barbeau, X.; Lague, P.; Bouchard, J. E.; Poirier, D. Discovery of a Non-Estrogenic Irreversible Inhibitor of 17beta-Hydroxysteroid Dehydrogenase Type 1 from 3-substituted-16beta-(m-carbamoylbenzyl)-estradiol Derivatives. J. Med. Chem. 2014, 57, 204-222.

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(30) Maltais, R.; Ayan, D.; Poirier, D. Crucial Role of 3-Bromoethyl in Removing the Estrogenic Activity of 17beta-HSD1 Inhibitor 16beta-(m-Carbamoylbenzyl)estradiol. ACS Med. Chem. Lett. 2011, 2, 678-681. (31) Ayan, D.; Maltais, R.; Roy, J.; Poirier, D. A New Nonestrogenic Steroidal Inhibitor of 17beta-Hydroxysteroid Dehydrogenase Type I Blocks the Estrogen-Dependent Breast Cancer Tumor Growth Induced by Estrone. Mol. Cancer Ther. 2012, 11, 2096-2104. (32) Trottier, A.; Maltais, R.; Ayan, D.; Barbeau, X.; Roy, J.; Perreault, M.; Poulin, R.; Lague, P.; Poirier, D. Insight into the Mode of Action and Selectivity of PBRM, a Covalent Steroidal Inhibitor of 17beta-Hydroxysteroid Dehydrogenase Type 1. Biochem. Pharmacol. 2017, 144, 149-161. (33) Maltais, R.; Trottier, A.; Roy, J.; Ayan, D.; Bertrand, N.; Poirier, D. Pharmacokinetic Profile of PBRM in Rodents, a First Selective Covalent Inhibitor of 17beta-HSD1 for Breast Cancer and Endometriosis Treatments. J. Steroid Biochem. Mol. Biol. 2018, 178, 167-176. (34) Los, G. V.; Encell, L. P.; McDougall, M. G.; Hartzell, D. D.; Karassina, N.; Zimprich, C.; Wood, M. G.; Learish, R.; Ohana, R. F.; Urh, M., et al. HaloTag: A Novel Protein Labeling Technology for Cell Imaging and Protein Analysis. ACS Chem. Biol. 2008, 3, 373-382. (35) Tremblay, M. R.; Poirier, D. Overview of a Rational Approach to Design Type I 17betaHydroxysteroid Dehydrogenase Inhibitors without Estrogenic Activity: Chemical Synthesis and Biological Evaluation. J. Steroid Biochem. Mol. Biol. 1998, 66, 179-191. (36) Sam, K. M.; Boivin, R. P.; Tremblay, M. R.; Auger, S.; Poirier, D. C16 and C17 Derivatives of Estradiol as Inhibitors of 17beta-Hydroxysteroid Dehydrogenase Type 1: Chemical Synthesis and Structure-Activity Relationships. Drug. Des. Discov. 1998, 15, 157-180. (37) Polavarapu, A.; Stillabower, J. A.; Stubblefield, S. G.; Taylor, W. M.; Baik, M. H. The Mechanism of Guanine Alkylation by Nitrogen Mustards: A Computational Study. J. Org. Chem. 2012, 77, 5914-5921. (38) Katzenellenbogen, J. A.; McGorrin, R. J.; Tatee, T.; Kempton, R. J.; Carlson, K. E.; Kinder, D. H. Chemically Reactive Estrogens: Synthesis and Estrogen Receptor Interactions of Hexestrol Ether Derivatives and 4-Substituted Deoxyhexestrol Derivatives Bearing Alkylating Functions. J. Med. Chem. 1981, 24, 435-450. (39) Rogers, G. A.; Shaltiel, N.; Boyer, P. D. Facile Alkylation of Methionine by Benzyl Bromide and Demonstration of Fumarase Inactivation Accompanied by Alkylation of a Methionine Residue. J. Biol. Chem. 1976, 251, 5711-5717. (40) Ruddraraju, K. V.; Zhang, Z. Y. Covalent Inhibition of Protein Tyrosine Phosphatases. Mol. Biosyst. 2017, 13, 1257-1279. (41) Glazer, A. N.; Delange, R. J.; Sigman, D. S. Chemical Modification of Proteins: Selected Methods and Analytical Procedures. In Laboratory Techniques in Biochemistry and Molecular Biology; Work, T. S.; Work, E., Eds.; Elsevier B.V.: 1976; Vol. 4, pp 135-166. (42) Shaw, E. Chemical Modification by Active-Site-Directed Reagents. In The Enzymes; 3 ed.; Boyer, P. D., Ed.; Academic Press: New York and London, 1970; Vol. 1, pp 91-146. (43) Laskowski, R. A.; MacArthur, M. W.; Moss, D. S.; Thornton, J. M. PROCHECK: A Program to Check the Stereochemical Quality of Protein Structures. J. Appl. Crystallogr. 1993, 26, 283-291. (44) Sawicki, M. W.; Erman, M.; Puranen, T.; Vihko, P.; Ghosh, D. Structure of the Ternary Complex of Human 17beta-Hydroxysteroid Dehydrogenase Type 1 with 3-hydroxyestra-1,3,5,7tetraen-17-one (Equilin) and NADP+. Proc. Natl. Acad. Sci. USA 1999, 96, 840-845.

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(45) Lin, S. X.; Yang, F.; Jin, J. Z.; Breton, R.; Zhu, D. W.; Luu-The, V.; Labrie, F. Subunit Identity of the Dimeric 17β-Hydroxysteroid Dehydrogenase from Human Placenta. J. Biol. Chem. 1992, 267, 16182-16187. (46) Kleywegt, G. J.; Jones, T. A. Phi/Psi-Chology: Ramachandran Revisited. Structure 1996, 4, 1395-1400. (47) Azzi, A.; Rehse, P. H.; Zhu, D. W.; Campbell, R. L.; Labrie, F.; Lin, S. X. Crystal Structure of Human Estrogenic 17β-Hydroxysteroid Dehydrogenase Complexed with 17βEstradiol. Nat. Struct. Biol. 1996, 3, 665-668. (48) Breton, R.; Housset, D.; Mazza, C.; Fontecilla-Camps, J. C. The Structure of a Complex of Human 17β-Hydroxysteroid Dehydrogenase with Estradiol and NADP+ Identifies Two Principal Targets for the Design of Inhibitors. Structure 1996, 4, 905-915. (49) Shi, R.; Lin, S. X. Cofactor Hydrogen Bonding onto the Protein Main Chain is Conserved in the Short Chain Dehydrogenase/Reductase Family and Contributes to Nicotinamide Orientation. J. Biol. Chem. 2004, 279, 16778-16785. (50) Mazumdar, M.; Fournier, D.; Zhu, D. W.; Cadot, C.; Poirier, D.; Lin, S. X. Binary and Ternary Crystal Structure Analyses of a Novel Inhibitor with 17beta-HSD type 1: A Lead Compound for Breast Cancer Therapy. Biochem. J. 2009, 424, 357-366. (51) Han, Q.; Campbell, R. L.; Gangloff, A.; Huang, Y. W.; Lin, S. X. Dehydroepiandrosterone and Dihydrotestosterone Recognition by Human Estrogenic 17βHydroxysteroid Dehydrogenase. J. Biol. Chem. 2000, 275, 1105-1111. (52) Breton, R.; Yang, F.; Jin, J. Z.; Li, B.; Labrie, F.; Lin, S. X. Human 17β-Hydroxysteroid Dehydrogenase: Overproduction Using a Baculovirus Expression System and Characterization. J. Steroid Biochem. Mol. Biol. 1994, 50, 275-282. (53) Zhu, D. W.; Lee, X.; Labrie, F.; Lin, S. X. Crystal Growth of Human Estrogenic 17β‐Hydroxysteroid Dehydrogenase. Acta Crystallogr. D Biol. Crystallogr. 1994, 50, 550-555.

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Figure 1. Three potent steroidal inhibitors of 17β-HSD1: 16β-(m-carbamoylbenzyl)-E2 (CC-156). 2methoxy-16β-(m-carbamoylbenzyl)-E2 (2-MeO-CC-156) and 3-(2-bromoethyl)-16β-(m-carbamoyl benzyl)17β-hydroxy-1,3,5(10)-estratriene (PBRM). 48x28mm (600 x 600 DPI)

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Figure 2. View of the active sites within the A subunit of 2-MeO-CC-156 (A) and PBRM (B) ternary complex structures. Inhibitor 2-MeO-CC-156 (F0A) and PBRM (F0D), and cofactor NADP+ are shown in their omit FoFc and 2Fo-Fc electron densities. The side chains of important residues Leu95, Ser142, Asn152, Tyr155, His221, and Glu282 are shown in their 2Fo-Fc electron densities. 2Fo-Fc maps draw in gray and contoured at 1σ; Fo-Fc maps draw in green and contoured at 2.5σ. The backbone of the A subunit in 2-MeO-CC-156 and PBRM complexes are shown in magenta and blue cartoon, respectively. 82x128mm (300 x 300 DPI)

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Figure 3. Superposition of A subunit of 2-MeO-CC-156 (magenta) and PBRM (blue) ternary complexes along with 17β-HSD1-CC-156-NADP+ (pink) at the binding sites, showing the inhibitors and important residues. A) Superposition of 2-MeO-CC-156 and CC-156 complexes at the steroid binding site. B) Superposition of PBRM and CC-156 complexes at the steroid binding sites. Interacting residues are labeled and shown in sticks. Hydrogen bonds of inhibitor 2-MeO-CC-156 and PBRM with their surrounding residues are presented in green dashed lines. Several important distances are labeled and indicated in black dashed lines. 82x131mm (300 x 300 DPI)

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